Document cross-wiki cache sharing logic.

[lhc/web/wiklou.git] / includes / Storage / SqlBlobStore.php

diff --git a/includes/Storage/SqlBlobStore.php b/includes/Storage/SqlBlobStore.php
index 72de2c9..d7216c5 100644 (file)
--- a/includes/Storage/SqlBlobStore.php
+++ b/includes/Storage/SqlBlobStore.php
@@ -94,7 +94,12 @@ class SqlBlobStore implements IDBAccessObject, BlobStore {
 
        /**
         * @param LoadBalancer $dbLoadBalancer A load balancer for acquiring database connections
-        * @param WANObjectCache $cache A cache manager for caching blobs
+        * @param WANObjectCache $cache A cache manager for caching blobs. This can be the local
+        *        wiki's default instance even if $wikiId refers to a different wiki, since
+        *        makeGlobalKey() is used to constructed a key that allows cached blobs from the
+        *        same database to be re-used between wikis. For example, enwiki and frwiki will
+        *        use the same cache keys for blobs from the wikidatawiki database, regardless of
+        *        the cache's default key space.
         * @param bool|string $wikiId The ID of the target wiki database. Use false for the local wiki.
         */
        public function __construct(
@@ -267,8 +272,7 @@ class SqlBlobStore implements IDBAccessObject, BlobStore {
 
                // No negative caching; negative hits on text rows may be due to corrupted replica DBs
                $blob = $this->cache->getWithSetCallback(
-                       // TODO: change key, since this is not necessarily revision text!
-                       $this->cache->makeKey( 'revisiontext', 'textid', $blobAddress ),
+                       $this->getCacheKey( $blobAddress ),
                        $this->getCacheTTL(),
                        function ( $unused, &$ttl, &$setOpts ) use ( $blobAddress, $queryFlags ) {
                                list( $index ) = DBAccessObjectUtils::getDBOptions( $queryFlags );
@@ -349,13 +353,32 @@ class SqlBlobStore implements IDBAccessObject, BlobStore {
                $blob = $this->expandBlob( $row->old_text, $row->old_flags, $blobAddress );
 
                if ( $blob === false ) {
-                       wfWarn( __METHOD__ . ": Bad data in text row $textId." );
+                       wfLogWarning( __METHOD__ . ": Bad data in text row $textId." );
                        return false;
                }
 
                return $blob;
        }
 
+       /**
+        * Get a cache key for a given Blob address.
+        *
+        * The cache key is constructed in a way that allows cached blobs from the same database
+        * to be re-used between wikis. For example, enwiki and frwiki will use the same cache keys
+        * for blobs from the wikidatawiki database.
+        *
+        * @param string $blobAddress
+        * @return string
+        */
+       private function getCacheKey( $blobAddress ) {
+               return $this->cache->makeGlobalKey(
+                       'BlobStore',
+                       'address',
+                       $this->dbLoadBalancer->resolveDomainID( $this->wikiId ),
+                       $blobAddress
+               );
+       }
+
        /**
         * Expand a raw data blob according to the flags given.
         *
@@ -370,7 +393,8 @@ class SqlBlobStore implements IDBAccessObject, BlobStore {
         * @param string|string[] $flags Blob flags, such as 'external' or 'gzip'.
         *   Note that not including 'utf-8' in $flags will cause the data to be decoded
         *   according to the legacy encoding specified via setLegacyEncoding.
-        * @param string|null $cacheKey May be used for caching if given
+        * @param string|null $cacheKey A blob address for use in the cache key. If not given,
+        *   caching is disabled.
         *
         * @return false|string The expanded blob or false on failure
         */
@@ -387,25 +411,22 @@ class SqlBlobStore implements IDBAccessObject, BlobStore {
                                return false;
                        }
 
-                       if ( $cacheKey && $this->wikiId === false ) {
-                               // Make use of the wiki-local revision text cache.
+                       if ( $cacheKey ) {
                                // The cached value should be decompressed, so handle that and return here.
-                               // NOTE: we rely on $this->cache being the right cache for $this->wikiId!
                                return $this->cache->getWithSetCallback(
-                                       // TODO: change key, since this is not necessarily revision text!
-                                       $this->cache->makeKey( 'revisiontext', 'textid', $cacheKey ),
+                                       $this->getCacheKey( $cacheKey ),
                                        $this->getCacheTTL(),
                                        function () use ( $url, $flags ) {
                                                // No negative caching per BlobStore::getBlob()
                                                $blob = ExternalStore::fetchFromURL( $url, [ 'wiki' => $this->wikiId ] );
 
-                                               return $this->decompressData( $blob, $flags );
+                                               return $blob === false ? false : $this->decompressData( $blob, $flags );
                                        },
                                        [ 'pcGroup' => self::TEXT_CACHE_GROUP, 'pcTTL' => WANObjectCache::TTL_PROC_LONG ]
                                );
                        } else {
                                $blob = ExternalStore::fetchFromURL( $url, [ 'wiki' => $this->wikiId ] );
-                               return $this->decompressData( $blob, $flags );
+                               return $blob === false ? false : $this->decompressData( $blob, $flags );
                        }
                } else {
                        return $this->decompressData( $raw, $flags );
@@ -461,7 +482,7 @@ class SqlBlobStore implements IDBAccessObject, BlobStore {
         * @note direct use is deprecated, use getBlob() or SlotRecord::getContent() instead.
         * @todo make this private, there should be no need to use this method outside this class.
         *
-        * @param mixed $blob Reference to a text
+        * @param string $blob Blob in compressed/encoded form.
         * @param array $blobFlags Compression flags, such as 'gzip'.
         *   Note that not including 'utf-8' in $blobFlags will cause the data to be decoded
         *   according to the legacy encoding specified via setLegacyEncoding.
@@ -469,10 +490,8 @@ class SqlBlobStore implements IDBAccessObject, BlobStore {
         * @return string|bool Decompressed text, or false on failure
         */
        public function decompressData( $blob, array $blobFlags ) {
-               if ( $blob === false ) {
-                       // Text failed to be fetched; nothing to do
-                       return false;
-               }
+               // Revision::decompressRevisionText accepted false here, so defend against that
+               Assert::parameterType( 'string', $blob, '$blob' );
 
                if ( in_array( 'error', $blobFlags ) ) {
                        // Error row, return false
@@ -486,7 +505,7 @@ class SqlBlobStore implements IDBAccessObject, BlobStore {
                        $blob = gzinflate( $blob );
 
                        if ( $blob === false ) {
-                               wfLogWarning( __METHOD__ . ': gzinflate() failed' );
+                               wfWarn( __METHOD__ . ': gzinflate() failed' );
                                return false;
                        }
                }